April 10 is national Siblings Day. Psychologist Dr. Kevin Leman is credited with understanding why your little brother is so annoying and why your oldest sister is so bossy. His best seller The Birth Order Book, updated in 2009, gives insight into how being an oldest, middle, or youngest child influences your personality, your career and your adult relationships.

I’m an oldest child. Social researchers say that being first born makes me more likely to be a self-disciplined Type A (check) and more ambitious (check.) In fact, researchers found that first born women are up to 13 percent more ambitious about their education and careers than first born men.

First borns usually experience more pressure to please their parents and succeed, so it’s probably no surprise that CEOs trend heavily toward first borns. A 2007 survey of 1,582 chief executives who are members of Vistage International, an executive performance company, revealed 43 percent of CEO respondents were the first born children. Middle children comprised 33 percent of CEOs; last-born siblings only 23 percent. Tuns out we are the boss of you.

Out of the first 44 presidents of the United States, 24 were first-born children or first-born sons. (A notable exception: George Washington, who had two older half-brothers.) Out of the first 23 American astronauts sent into space, 21 were first-born children.
Since the oldest child usually gets the blame for not only what they do, but also for failing to keep younger siblings out of trouble, we also have a big streak of conscientiousness. We tend to boss people around and take charge, and feel guilty when projects don’t work out, even if we weren’t at fault.

Middle children, who usually face less pressure in families to perform, tend to be happier in their adult relationships and self-identify as more relaxed. Because they have to get good at reading signals from siblings, they often have better negotiating and social skills and excel at team sports (including business.)

Youngest children may have an advantage in creative thinking, according to Adam Grant in his latest book, Originals: How Non-Conformists Move the World. Grant writes that younger siblings tend to take more intellectual and physical risks than their perfectionist and conservative oldest siblings. In a study of professional baseball players, younger children were 10.6 times more likely to attempt stealing bases than their older siblings.

First borns start out making more money than their middle or youngest siblings, but that advantage is usually wiped out by about the age of thirty. That’s because last born children tend to jump around in their careers more, skipping from job to job more often to take advantage of higher paying opportunities.

Grant also writes that youngest children often choose unconventional careers in order to “compete by not competing.” Grant analyzed Comedy Central’s 2004 list of the greatest comedians of all time; of the 100 names on the list, 44 were last born. Only 20 were first born; statistically, the number should be about equal. Being the oldest child, apparently, is no laughing matter.

Your birth order is not destiny, of course. But you may be more influenced by your siblings than you imagined. Give your youngest brother an extra dutch rub when you see him this weekend.